Many image forming devices, such as printers, available in the market have ribbon mechanisms for providing ribbon strips mounted thereon to be used for forming images on printing mediums passed through the printers. A conventional ribbon mechanism often includes a support frame having a pair of supply spindles respectively mounted on opposite plates (left and right) on the support frame, and a pair of take-up spindles also respectively mounted on opposite plates (left and right) on the support frame. A ribbon roll is mounted on the supply spindles for providing the ribbon strip to a conventional printer. Underneath the support frame, a print head is movably coupled to the bottom of the support frame of the conventional ribbon mechanism by a resilient means, i.e., in a sense, the print head is floating under the support frame of the conventional ribbon mechanism. Normally, the conventional ribbon mechanism is coupled to a drive part of the conventional printer. The drive part is ordinarily positioned under the ribbon mechanism in the conventional printer and is pivotally coupled to the ribbon mechanism by a pivot means. Thus, the conventional ribbon mechanism may be pivotally opened from the drive part for threading the continuous ribbon strip of the ribbon roll between the ribbon mechanism and the drive part.
The ribbon roll is formed by winding and wrapping the continuous ribbon strip over a cylindrically shaped roll holder. To load the ribbon strip in the printer, the roll holder is engaged to the pair of supply spindles at both ends of the ribbon mechanism for holding the ribbon roll. Thereafter, the ribbon strip is pulled from the ribbon roll toward a back end of the conventional ribbon mechanism, behind and underneath the ribbon mechanism to cover the print head, and proceeding upward at a front end of the ribbon mechanism toward a take-up roll holder. The take-up roll holder is mounted on the take-up spindles and is adapted to wind up the ribbon strip to finish loading of the ribbon strip in the conventional printer. As a result, a ribbon path of every conventional printer is defined by the ribbon strip originating from the ribbon roll and ending up at the take-up roll holder via the underside of the conventional ribbon mechanism.
The drive part of the conventional printer contains a platen for pressing the printing medium and the ribbon strip against the print head to facilitate the print head forming images on the printing medium. The platen is of cylindrical shape and the print head often includes a flat panel circuit board capable of converting electrical data to thermal coding information. Normally, the printer has a gear system coupled between the platen and a motor of the printer. The motor is adapted to drive the gear system, which, in turn, rotates the platen at a speed according to gear ratios among gears of the gear system. In addition, the platen presses the printing medium and the ribbon strip against the print head sufficiently tight that when the platen rotates, the printing medium and the ribbon strip will be driven tangentially between the platen and the print head. Thus, the printing medium and the ribbon strip may be moved through the printer by rotating the platen.
As stated, the drive part is pivotally coupled to the ribbon mechanism of the conventional printer. For better alignment between the platen and the print head, the print head is resiliently coupled to the ribbon mechanism. The ribbon mechanism is adapted to be pivotally opened from the drive part for loading or unloading the printing medium, but the ribbon mechanism could not move laterally or vertically with respect to the drive part. The floating arrangement between the print head and the support frame of the ribbon mechanism provides some advantages to the conventional printer. For instance, it allows the print head to be adjustably positioned with respect to the position of the platen. Thus, the floating arrangement of the print head under the support frame provides freedom of motion for better alignment between the print head and the platen.
Normally, the platen is slightly longer than the print head in order not to miss printing of images on the printing medium. It is essential for the platen to press along the print head with even force for producing good quality printouts. Otherwise, any slight misalignment between the print head and the platen might cause the platen to exert uneven force along the print head and might greatly reduce the quality, e.g., the clarity or the sharpness, of images formed on the printing medium. The misalignment might also increase the propensity of wrinkling the ribbon strip and might further degrade the quality of the images formed on the printing medium. In addition, some conventional printers connect the print heads to their respective platens using single brackets within the conventional printers. The single-bracket design of some conventional printers helps reduce possibilities of misalignment for these conventional printers during operation. However, although great efforts have been taken by all printer manufacturers, it is still difficult to precisely align a print head with a platen in a conventional printer during assembly of the printer. Any imperfection, however slight, of aligning the platen with the print head during the printer assembly may potentially cause many adverse effects on printing quality. By having a floating print head design, the requirement for a precise alignment between the platen and the print head during assembly is greatly alleviated. Thus, when the platen presses against the floating print head during operations of the printer, the print head will be forced to readjust its orientation or position relative to the position of the platen for a better alignment. As a result, having a floating print head under the conventional ribbon mechanism will improve the alignment of the print head with the platen during operations, even though the print head and the platen might not be precisely aligned when originally assembled.
The floating print head design of the ribbon mechanism is, however, not without drawbacks to the conventional printer. More particularly, the conventionally designed ribbon mechanism often could not simultaneously align with the print head and the platen, and therefore the ribbon strip mounted on the ribbon mechanism often could not simultaneously align with the ribbon mechanism and the platen during operation as well. That is because most conventional printers' print heads are approximately aligned with their respective ribbon mechanisms when assembled. Therefore, the print head of the conventional printer is usually aligned with the ribbon mechanism only in a loading position, i.e., when the ribbon mechanism is pivotally disengaged from the drive part of the printer and does not touch the platen. For the conventional printer, although the ribbon mechanism is pivotally coupled to the drive part for opening, the support frame of the ribbon mechanism could not adjust its orientation or position relative to the drive part when the ribbon mechanism is closed against the drive part for operation. Normally, the platen is fixedly positioned within the drive part of the conventional printer and will not change its orientation or position with respect to the ribbon mechanism either. As a result, if the print head has to readjust its orientation or position in order to align with the platen, the print head will not be able to maintain sufficient alignment with the conventional ribbon mechanism required for generating acceptable printing quality and ribbon handling.
Moreover, any misalignment between the print head and the ribbon mechanism will potentially cause problems to the ribbon strip. As stated, the ribbon strip is threaded between the print head and the platen. The ribbon path is defined by the ribbon strip originating from the ribbon roll mounted on the supply spindles, proceeding to the underside of the ribbon mechanism at the back end, and moving up at the front end of the ribbon mechanism to be wound by the take-up roll holder mounted on the take-up spindles. If the print head is misaligned with the ribbon mechanism, the ribbon strip will also be forced by the print head to misalign with the ribbon mechanism by virtue of being pressed against the print head by the platen from underneath. When it is misaligned, a part of the ribbon path between the ribbon roll and the print head will therefore be slightly twisted. As a result, a cross section of the ribbon strip that touches the print head during printing could no longer be evenly driven by the platen. Different areas of the misaligned ribbon strip will thus experience unequal net driving forces when moving through the printer and the ribbon strip will therefore experience uneven stress. As a consequence, one end of the misaligned ribbon strip might be pulled with more force than an opposite end of the ribbon strip due to the misalignment. Thus, the uneven stress on the ribbon strip due to misalignment will often result in wrinkles to the ribbon strip and might render poor printing quality to the printing medium. Therefore, an improved ribbon mechanism is needed to provide better and simultaneous alignments for the ribbon strip both with the print head and with the platen.